I think the best way is to apply opacity to the background of the TR and leave the TD.

From W3schools:

When using the opacity property to add transparency to the background
of an element, all of its child elements become transparent as well.
This can make the text inside a fully transparent element hard to
read. If you do not want to apply opacity to child elements, use RGBA
color values instead (See "More Examples" below).
http://www.w3schools.com/cssref/css3_pr_opacity.asp